120 MKSOZOIC FLOK'AS OF rMTED STATES. 



leaf svibstance. This indicates that the nerves are disclosed only on 

 the lower snrface. The nervation resembles that of Xeuropteris of 

 the Carbonifei'ous, but tliere is no niidnerve visible, although it may 

 be present, as the nervation is not fully disclosed. The nerves appear 

 to radiate from the Ijase of the fossil, and they fork several times. The 

 surface of the coal film, which represents the supposed l:)ract, is granu- 

 lated witli ininut(> papilla' of no definite form. They may l)e due to 

 the shrinking of tlie leaf. The general aspect of these fossils suggests 

 that they may be l)racts of the involucre of some ^^'illiamsonia. Tlie 

 three found are apparently essentially the same, but present some unim- 

 portant differences in form, which are shown in the figures given. They 

 are distinguished as a, h, c. 



Bract a is elliptical in form and not symmetrical, one lateral margin 

 being more strongly convex than the other. It tapers gradually to a 

 sul)acute tip, which is well shown. The ))ase is imperfect. I^ract b 

 is of the same general form, but is broader and propt)rtionally shorter. 

 The basal portion is wanting. Bract c is ovate elliptical and nearly 

 symmetrical in form. 



PI. XXIX, Fig. 8, represents bract a, enlarged in Fig. 9; Fig. 10 

 bract b, and Fig. 11 bract c, enlarged in Fig. 12. 



Order GINKGOALES. 



Family (aNKGOACE.F]. 



Genus GINKGO Ka.Mupfer. 



The Ginkgos of the Oregon Jurassic are the most important fossils 

 in it. This is due to the fact that they show a great mmil)er of speci- 

 mens and a very considerable variety of forms, which are quite well 

 preserved. The leaves are preserved mostly entire, and the condition 

 in which they may he ol)tained depends on the splitting of tlie rock 

 containing them. Unfortunately the cleavage of this is generally poor, 

 othei-wise very perfect specimens might be ol)tained in greater num- 

 bers. At some of the localities the impi'ints of Ginkgo leaves are 

 exceedingly numerous and may be obtained by the hundreds. The 

 faces of the rock, when exposed by splitting it, are covered with numer- 

 ous impressions, often of diffeictil character or type, while the variation 

 in the leaves is considerable. 1 am not sure that they are not all modi- 



